(1) Field of the Invention
This invention relates to a wire bonding gold line used for interconnecting a semiconductor tip electrode and an outside lead portion.
(2) Description of the Prior Art
The gold lines heretofore used for TC bonding methods as disclosed in the Official Gazette of Japanese Patent No. Sho 54-24265 contain gold having a purity level of 99.995 wt% and between about 0.0003-0.0030 wt% of germanium(Ge). The germanium is included to minimize the effect of impurity elements and to reduce the electric resistance by improving further the purity of itself.
However, when the purity of said gold line is improved, in this manner the additional amount of germanium weakens the mechanical strength of the gold line. Hence, it was found that the gold line often tends to break during wire drawing, such that the yield is degraded. In addition, other problems tend to occur during bonding.
Inasmuch as the additional amount of said germanium enhances properties of the gold line as to elongation elongation, the presence of germanium tends to reduce the strength of the gold and reduce its malleability. Thus, the loop shape becomes less stable. In addition, problems are encountered because of reduced bonding strength and more neck breakage tends to take place.
It has been observed, however, that when the additional amount of germanium is increased to amounts exceeding 0.006 wt%, the elongation properties become somewhat reduced but the strength of the alloy increases. Nevertheless, the problem is that the gold line becomes too hard and the bonding strength in a second bonding portion is weakened which tends to result with defective bonding. Accordingly, prior attempts to improve gold alloys for this purpose have not resulted with an acceptable alloy from the standpoint of satisfactory mechanical strength in addition to the respective elongation and strength properties.